1. Trawl – Species Composition Sampling
Trawl – Species Composition Sampling
INSERT INSTRUCTOR Name
Shrimp trawler:
Mauritanian trawler: - Courtesy of Joël Prado - FAO/FIIT
Chinese trawlers:
Joël Prado - FAO/FIIT

2. Sampling Priorities Collect information on fishing effort
Randomly sample for catch composition
Record gear characteristics
Collect length-frequency data on target and non-target catch

3. Objectives List 4 things that can effect species composition sampling
Demonstrate ability to select & describe appropriate sampling method
Demonstrate ability to complete the Catch Composition form

4. Effects on sampling Vessel size / layout Tow duration Catch size
Effects on sampling
Vessel size / layout
Tow duration
Catch size
Catch composition - target
Sorting techniques
Big codend photo:
Shrimp bycatch (madagascar):
Shrimp trawl
(Madagascar)

5. Catch composition Multiple sets/day – how to choose? Observer logbook
Sets/day Random sample table (RST) None – Sample all sets
3-4 RST#1
5+ RST#2
How much to sample?
Diversity of catch (size, # species)
Time before next haulback

6. on length collection list?4
Total catch estimated
by 2A /2B or 2C?
4B i. Set aside all retained catch
ii. Randomly select 1-2 baskets of discards for species composition of discards.
iii. Sort the species composition sample into smaller baskets by species or species group. Go to #5.
4A i. Randomly select 1-2 baskets.
ii. Sort the species composition sample into smaller baskets by species or species group. Go to #5
2A/2B
Unsorted
2A/2B
Sorted 2C 4C
i. Select a minimum of 4 unsorted baskets for a density sample;
ii. Select all or part of the density sample for species composition sample;
iii. Sort the species composition sample into smaller baskets by species or species group. Go to #5.
5 Is this a species
on length collection list?
HINT: Start with
target spp. 5A
i. Count / weigh each species.
ii. Estimate the proportion retained for
each spp.
iii. Randomly collect a predetermined # of individuals, determine gender & measure lengths
iv. Return target species to crew for
processing & discard non-retained
species.
Go to 6
Yes 5B
i. Count / weigh each species.
ii. Estimate the proportion retained for
each spp.
iii. Return target species to crew for
processing & discard non-retained
species.
Go to 6 No
Yes 6
More spp? No
Done
Species Composition – Figure 6-18
Species Composition

7. Weight all catch – no sorting
24.3 kg
23.3 kg
23.2 kg
24.6 kg
23.3 kg
27.7 kg
22.8 kg
22.9kg
23.2 kg
24.7 kg
25.6kg
24.6 kg
24.4 kg
15.4 kg
Σ basket weights = kg
Randomly select 3 baskets for spp comp – sample weight = 71.1 kg

8. on length collection list?4
Total catch estimated
by 2A /2B or 2C?
4B i. Set aside all retained catch
ii. Randomly select 1-2 baskets of discards for species composition of discards.
iii. Sort the species composition sample into smaller baskets by species or species group. Go to #5.
4A i. Randomly select 1-2 baskets.
ii. Sort the species composition sample into smaller baskets by species or species group. Go to #5
2A/2B
Unsorted
2A/2B
Sorted 2C 4C
i. Select a minimum of 4 unsorted baskets for a density sample;
ii. Select all or part of the density sample for species composition sample;
iii. Sort the species composition sample into smaller baskets by species or species group. Go to #5.
5 Is this a species
on length collection list?
HINT: Start with
target spp. 5A
i. Count / weigh each species.
ii. Estimate the proportion retained for
each spp.
iii. Randomly collect a predetermined # of individuals, determine gender & measure lengths
iv. Return target species to crew for
processing & discard non-retained
species.
Go to 6
Yes 5B
i. Count / weigh each species.
ii. Estimate the proportion retained for
each spp.
iii. Return target species to crew for
processing & discard non-retained
species.
Go to 6 No
Yes 6
More spp? No
Done
Species Composition – Figure 6-18
Species Composition

9. Catch composition – sorted catch
Weigh all retained
By species (sample type 3A)
Mixed bags (sample type 3B)
Subsample discards for composition
Weigh all baskets
Weigh subsample of baskets
Randomly select a few baskets for spp comp of discards (sample type 3C)

10. Weigh all catch – sorting
Retained – spp known
Retained – mixed
Discard
Spp A
59.3 kg
Spp E
7.6 kg
18.4
20.1
18.4
20.1
Spp B
45.5 kg
Spp F
6.8 kg
22.6
22.6
27.3
Spp C
25.2 kg
Spp G
4.3 kg
23.4
23.4
23.4
21.9
Spp D
20.3kg
Spp H
1.5 kg
22.2
22.2
24.3
24.3
Total catch = Σ retained + Σ discard = = 457.4
Sample Type (ST) 3A = kg
ST 3B = 23.4 (of in the mixed baskets)
ST 3C = 24.3 (of in discard baskets)

11. Discards
27.2
26.1
23.6
24.4
27.1
23.4
25.9
23.5
27.7
23.6
25.4
27.0
25.9
26.8
27.7
26.1
27.9
27.4
23.4
23.9
24.8
23.6
25.8
26.2
27.1
25.5
26.2
27.7
23.9
24.4
24.4
25.1
24.5
23.5
25.4
23.4
Fill evenly – randomly select 10 for weight sample & 3 for spp comp
Σ basket weights / # baskets weighed = / 9 =
Total count * average = 28 * = kg
Actual = kg

12. Discards Select 2 baskets for discard composition
27.2
23.6
23.6
23.6
23.4
25.4
27.0
25.9
25.9
26.8
27.7
26.1
26.1
27.9
27.4
23.4
23.4
23.9
24.8
23.6
23.6
25.8
26.2
27.1
27.1
25.5
26.2
27.7
27.7
23.9
24.4
24.4
24.4
25.1
24.5
23.5
23.5
25.4
23.4
Select 2 baskets for discard composition
ST 3C = = 47.0 kg

13. Catch composition – helpful hints
Remember to include any items or specimen removed prior to taking the catch composition sample on the catch composition form as sample type 1 or 8
If the vessel is changing nets throughout a trip, it may be helpful to mark nets for easy identification

14. Sampling description Most trawl samples require extensive subsampling
Systematic spatial with a random start;
Random spatial
Systematic Temporal and
Random Temporal

15. Sampling description Most trawl samples require extensive subsampling
Systematic spatial with a random start;
Random spatial
Observer logbook - p 12
Define population
Describe sample frame type & units
Describe how random numbers were generated
Describe the sample method
Multiple levels

16. Sampling description 2. Within Haul Composition Sampling:
Population: individuals in a haul (all codends combined)
Sampling Frame Type and Units: Spatial sample frame – baskets; divide all mix or all discards into equal size baskets and select one or more baskets for comp. sample.
Expected number (range) of sampling units in population: sorted retained – all weights verified, counts from crew; mixed species retained catch (small fish) – 2-6 baskets; discard catch – 8-20 baskets
Random numbers generated by: dice, Random number table
Sampling Method: All of the larger fish & shrimp were sorted/weight by species and their weights are verified/recorded. Smaller fish and discards are subsampled for composition. For mixed fish retained sample, randomly select 1 bag/basket of 4-6 total for species specific assessment; for discard sample, randomly select 1 basket of 8-20 baskets for composition sample.
 Describe any factors that affected your random sample: 1-crew sometimes forgot to keep all discards and threw some things overboard as they were sorting; 2-shovels are small so sometimes the larger discards get pushed around before they are eventually lifted into the discard baskets;

17. Catch Composition Form

18. Catch Composition Form

19. Catch Composition Form

20. Catch Composition Form
Weights
Actual
Average weight
Estimate

21. Catch Composition Form

22. Catch Composition Form

23. Activity Spit into groups Create a sampling plan for a diverse haul
Make measurements of either the bin or codend
Each of you will complete the catch composition form, sampling description & total catch estimation

24. Summary
What are four things that can affect a sample?